As an abnormal combustion in a cylinder of an internal combustion engine, a preignition is well known. The preignition is a phenomenon in which air-fuel mixture in a cylinder is self-ignited earlier than a proper ignition timing. In a case where a portion close to an ignition plug is a heat source, the preignition is continuously generated. In a case where suspended matters such as oil droplets and carbon deposits are the heat source, the preignition is suddenly generated.
JP-2013-221413A (DE-102013205795A1) shows an abnormal-combustion detecting device which is provided with a preignition detecting portion which determines whether a preignition is generated, and a preignition identification portion which determines whether the preignition is suddenly generated due to the suspended matters in a cylinder. Moreover, when a sudden preignition is detected, the abnormal-combustion detecting device executes a fuel-quantity-increase control in which a fuel injection quantity is increased, so that the generation of the preignition is restrained.
In the above abnormal-combustion detecting device, after the preignition is actually generated, the fuel-quantity-increase control is executed for suppressing the successive preignitions. Therefore, it is impossible to prevent the generation of the preignition, beforehand. Moreover, the fuel-quantity-increase control causes an increase in fuel consumption.